Calorimetric studies on interactions of divalent cations and microorganisms or microbial envelopes

The biosorption of heavy metal ions has attracted serious attention as a biotechnological approach to the removal of these elements from effluents or to the recovery of precious metals and radionuclides. We compared the metal sequestering capability of Bacillus subtilis, Saccharomyces cerevisiae and other strains, and determined sorption equilibria of the reaction M + L reversible arrow ML and the corresponding heats of reaction. The strains showed typical capacities and affinities to a series of metal ions but no clear selectivities. Adsorption was slightly endothermic and very fast and was driven by large T Delta S contributions. The data provide a critical view of the technical applicability of biosorption.